How do you classify the various Computers?-Describe the Internal parts of CPU?-What is RAM? What are its functions? -What is ROM? What are its functions and features?


1. How do you classify the various Computers?


Computers can be classified into two categories on the basis of the type of data they are designed to process. Data may be obtained either as a result of counting, in which case it is called as discrete data or by using some continuous signal measuring instruments, in which case it is called continuous data.



The classification of computers on the basis of type of data is as follows:


1. Digital Computers: These computers operate on discrete data and are commonly used in business applications. Digital computers can be further classified into general purpose and special purpose computers.


 General purpose Computers: A general purpose computer is one that can be used for a variety of applications. Its versatility enables execution of programs of almost any time. These are used in business applications.


Special Purpose Computers: These are designed to perform a specific task. Such computers lack versatility. They perform the task for which they are designed very efficiently. E.g. Air craft control system, missile guidance system etc.


2. Analog Computers: This type of computers work on continuous data measured along a continuous scale. E.g., a speedometer is a mechanical device that works on a continuous data. Analog computers are used in process control systems which monitor pressure, temperature etc.


3. Hybrid Computers: This type of computers combines the properties of both analog and digital computers. A typical example is found in medicine where analog properties are sued to record the patient’s data, while digital properties help in the analysis of the data as well as in monitoring the patient’s health.   Computers are also classified on the basis of their physical size, memory and processing speeds.


Five of these categories are described below:


1. Micro computers: These are based on the use of micro processors. A microprocessor is a programmable large scale integrated circuit chip containing all the elements required to process binary encoded data. A micro computer performs all arithmetic and logical functions of a computer. They are also referred as personal computers.


2. Mini Computer: These systems are more powerful than micro computers and are also more expensive. The word length is generally 16 bits or more. The processing speed of a computer is often measured in terms of MIPS-Millions of Instructions per Second.


3. Super mini computers: These are faster than mini computers. The word length is generally 32 bits and processing speed is more than 1.5 MIPS. These systems have efficient time sharing operating systems with multiprogramming features.


4. Mainframe computers: These are machines with word length of 32 bits or more. The processing speed is of the order of 10 MIPS. These computers support a large main memory. In the time sharing mode, due to fast processing speed, they can support hundreds of terminals. Memory size may be 10Mb to 128 Mb.


5. Super Computers: They are the fastest computers and can be used to solve a wide range of large scale problems which require extensive numeric computations like complex molecular structural analysis, weather forecasting etc. The processing speeds are of the order of 100 MIPS. These machines have word lengths of 64 bits or more. These computers have a very large memory, ranging from 8 Mb to 10 gigabytes.


2. Describe the Internal parts of CPU?


The CPU has two main parts:


1. The Control Unit.


2. Arithmetic Logic Unit.


The main two parts of the CPU are usually connected by an electronic component referred to as a Bus, which acts as an electronic highway between them. The CPU has special purpose storage devices called registers, helps in storing data and instructions. The two major parts along with Bus & Registers are described here as below:


 Control Unit: It is responsible for directing and coordinating most of the computer system activities. It does not execute instructions by itself. It tells other parts of the computer system what to do. It determines the movement of electronic signals between the main memory and arithmetic logic unit as well as the control signals between the CPU and input/output devices.


 Arithmetic logic Unit: ALU performs all the arithmetic and logical functions i.e. addition, subtraction, multiplication, division and certain comparisons. These comparisons include greater than, less than, equals to etc. The ALU controls the speed of calculations.


 Registers: It is a special temporary storage location within the CPU. Registers quickly, accept, store and transfer data and instructions that are being used immediately (main memory hold data that will be used shortly, secondary storage holds data that will be used later). To execute an instruction, the control unit of the CPU retrieves it from main memory and places it onto a register. The typical operations that take place in the processing of instruction are part of the instruction cycle or execution cycle. The instruction cycle refers to the retrieval of the instruction from main memory and its subsequence at decoding. The process of alerting the circuits in CPU to perform the specified operation. The time it takes to go through the instruction cycle is referred to as I-time.


 Bus: The term Bus refers to an electrical pathway through which bits are transmitted between the various computer components. Depending on the design of the system, several types of buses may be present. The most important one is the data bus, which carries the data through out the central processing unit. The wider the data bus, the more data it can carry at one time and thus the greater the processing speed of the computer. Ex: Intel 8088 processor uses a data bus of 8 bits wide. Some super computers contain buses that are 128 bits wide.


3. What is RAM? What are its functions?


The main memory of the computer is called as Random Access Memory (RAM). The name derives from the fact that data can be stored in and retrieved at random, from anywhere in the electronic main memory chips in approximately the same amount of time, no matter where the data is. Main memory is in an electronic or volatile state. When the computer is off, main memory is empty, when it is on it is capable of receiving and holding a copy of the software instructions, and data necessary for processing.   Because the main memory is a volatile form of storage that depends on electric power can go off during processing, users save their work frequently on to non volatile secondary storage devices such as diskettes or hard disk.


The main memory is used for the following purposes:


1. Storage of the copy of the main software program that controls the general operation of the computer. This copy is loaded on to the main memory when the computer is turned on, and it stays there as long as the computer is on.


2. Temporary storage of a copy of application program instruction, to be received by CPU for interpretation and processing or execution.


3. Temporary storage of data that has been input from the key board, until instructions call for the data to be transferred in to CPU for processing.


4. Temporary storage of data, which is required for further processing or transferred as output to output devices such as screen, a printer, a disk storage device.


4. What is ROM? What are its functions and features?


Instructions which are critical to the operation of a computer are stored permanently on Read only Memory (ROM) chip installed by the manufacturer inside the computer. This ROM chip is also called firm ware, retains instructions in a permanently accessible nonvolatile form. When the power in the computer is turned off, the instructions stored in ROM are not lost.


It is necessary and also convenient to have instructions stored in ROM. The more instructions in ROM, the fewer diskettes you may have to handle. Until recently the process of manufacturing ROM chips and recording data on them was more expensive than the process of producing RAM chips. As a result the manufacturers tended to record in ROM only those instructions that were crucial to the operation of the computer.


Today, due to improvements in the manufacturing process of ROM chips have lowered the cost to the point where manufacturers are beginning to include additional software instructions. In addition to ROM, three additional categories of non volatile memory are used in some computer systems. They are PROMs, EPROMs, and EPROMs. PROM stands for programmable read only memory.It works similar to that of ROM. PROM chips are custom made for the user by the manufacturer. The user determines what data and instructions are to be recorded on them. The data on PROM is permanent and cannot be erased.   Erasable programmable read only memory (EPROM), developed as an improvement over PROM. The data on the EPROM can be read with the help of a special device that uses ultra violet light.


The data or instructions on the EPROM are erasable and new data can be entered in its place. EPROM functions exactly same as PROM.   Electronically erasable programmable read only memory (EEPROM) avoids the inconvenience of having to take chips out of the computer to change data and instructions. Changes can be made electrically under software control. These are used in point of sale terminals to records price related data for products. The prices recorded on them can be easily updated as needed. The only disadvantage of EEPROM is, the regular ROM chips.

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